A mobile magneto-optical disk system with 2 Gbytes user- capacity is proposed. The disk consists of a center aperture detection type of magnetically induced super-resolution medium, a 0.5 mm thickness substrate with 50 mm in diameter, and a newly developed UV curing resin film to keep the disk tilt small even if its surrounding environmental condition changes. The optics contains a blue laser diode of a 406 nm wavelength and an objective lens with a numerical aperture of 0.6. A laser pulsed magnetic field modulation method is employed and it realizes land and groove recording with an effective track pitch of 0.40 micrometers . Practicable system margin values are confirmed at 0.146 micrometers bit density.
A 6 GB user-capacity disk with a 120 mm-diameter single side substrate was realized by the use of a center aperture detection (CAD) type of magnetically induced super resolution (MSR) disk through the AS-MO (Advanced Storage Magneto Optical) activity. It utilized a practical optics which consists of a 640 nm wavelength laser and a 0.6 numerical aperture (NA) lens, and land and groove (L/G) recording with an effective track pitch of 0.6 pm was realized. The areal bit density reached to 4.6 Gbit/in<sup>2</sup> with available system margins. In this report, we present improved CADMSR performance at narrower pitch tracks and at higher linear density with the same optics.
We manufactured a high-frequency wobbled groove disk, and examined reading/writing a magneto-optical signal by using a clock generated from the wobbled groove. We also measured clock jitter and bit error rate. The results of this were clock jitter of under 2.5 ns, and a bit error rate almost equal to that of a self-clock. This wobbled groove clock method is therefore effective for higher density recording.
To reduce recording magnetic field of a magneto-optical super-resolution disk which uses an in-plane magnetization readout layer, we developed a new disk structure. By preparing a DyFeCo intermediate layer between the readout layer and the recording layer, the recording magnetic field was greatly reduced and then both super-resolution readout and mark-edge recording by a magnetic field modulation method were achieved. By using the new triple-layered disk for super-resolution readout, a carrier to noise ratio of 45 dB at a 0.4 micrometers mark length was obtained and the recording magnetic field became 15 kA/m.